- Analysis and assesment of provisioning and regulating ecosystem services in mixed forests
- Forest Growth and Yield Models
- Management impact on forest ecosystems
Summary of research
During MsC studies I won an Undergraduate fellowship in the Department of Applied Physics I to work with remote sensing images to estimate forest attributes, after having finished MsC in Forestry at University of Valladolid I was granted by INIA for one year to work on applications of National Forest Inventory (NFI) data, final results of these two-year period was published as a book chapter (Bravo-Oviedo and Delgado de la Mata, 2002) in which I built a model to estimate wood volume in P. sylvestris L. stands from Normalized Difference Vegetation Index obtained by remote sensing and data from NFI. In 2002 I was granted by the Ministry of Science and Technology to start my PhD within the project AGL2001-1780 (Pinus pinaster Ait. stand Dynamics in the Southern Iberian Mountain Range: Genetic structure, regeneration and forest dynamics). The topic of the PhD was the development of an individual-based model for Pinus pinaster Ait. in Southern Iberia Range (Spain). In 2003 I spent a two-months period at the University of Applied Science in Vienna under the supervision of Prof. Dr. Hubert Sterba to learn how to model tree survival. At the same time I was animated to build a stand growth model for the same species with data from INIA-CIFOR permanent sample plots and I published the first dynamic growth model for P. pinaster in Spain including site index curves, which are used to classify stands in potential wood productivity classes (Bravo-Oviedo et al. 2004). Results for the height growth pattern opened the possibility to study differences in growth pattern by regions as two markedly different growth patterns were identified as plausible: polymorphic with common asymptote, and anamorphic with free asymptote. The model also indicated that initial state variables correctly served as proxies of site conditions to project basal area and volume under common silvicultural treatments.
By the end of 2004 there was a job opportunity to join INIA-CIFOR as a Research Collaborator. I applied for the position and I finally won it in 2005 and later promoted to Research Assistant in 2008. Consequently I had to put aside my initial scientific career. However, as I had demonstrated my capacity for research I was permitted to continue publishing scientific results. During 2005 I collected data necessary to model growth at tree level, including soil data. Because of my initial interest in environment-growth relationships Dr. Gregorio Montero, who was my co-advisor in INIA-CIFOR, offered me the possibility to profit lessons from the extension course in Multivariate Analysis by relating soil attributes with site index in stone pine stands (P. pinea L.) (Bravo-Oviedo et al. 2005). For the first time, perceptual maps of correspondence analysis was presented in forestry literature. The graphs indicate that there were a strong association between low site index classes, clay and impermeable soils. The relation between soil texture and site index classes was weaker in high site index classes, indicating that in areas with the same climate conditions, differences in soil texture are the main environmental factors affecting growth. One of the main results in my career during this period was the assessment of competition-induced mortality for P. pinaster Ait. and P. sylvestris L. (Bravo-Oviedo et al. 2006). This comparative study showed the differential survival rate of both species and the factors affecting them. Two kind of competition induced mortality in P. pinaster: asymmetric or light-competition represented by the social position of a tree within the stand and competition for below ground resources (symmetric competition) indicated by the cross-sectional dimension of each tree (basal area). For P. sylvestris L. partial asymmetric competition was identified as the main driver of mortality because of the important role of size inequality.. In 2007 I resumed my Ph.D. and I focused on individual tree dominant height-growth and its relation with climate and soil and applying relevant new methodologies in growth modeling like Generalized Algebraic Difference Approach (GADA) I proposed a new method for assessing local and global parameters in site index equations (Bravo-Oviedo et al. 2007). The method consisted of plotting initial parameter estimates against a surrogate of the growth intensity factor (a key concept in the GADA methodology). The surrogate is the actual site index, namely the true dominant height at any base-age obtained from sample trees. In order to avoid base-age dependency, which it is an unwanted constraint, the relation was found to be invariant across different base-age. The application of this method facilitates the selection of an appropriate GADA expression reducing the alternatives and assisting growth hypothesis. The paper also revealed some inter-regional variability in height growth pattern, although the factors that might have led to such variation were not identified. This lack of known factors for explaining height growth variation was a debatable issue during my international training in Portugal [IT.4] at Istituto Superior de Agronomia under the supervision of Dr. Margarida Tomé. As a fruitful collaboration and understanding with her I developed a GADA model in which local climate and lithology was incorporated in the model formulation (Bravo-Oviedo et al. 2008). This implies that the height growth model becomes local, as opposed to regional which means more flexibility and growth options, for example it allows different growth trajectories for two stands with the same initial age and initial height but different climate and/or lithology. This was the first time that environmental information was incorporated explicitly in GADA methodology and it has been replicated by in other species. The model was a climate-based model and I explored, in close collaboration with Dr. Clemente Gallardo-Andrés from the Instituto de Ciencias Ambientales of University of Castilla-La Mancha, the applicability of the climate-based model with data from Regional Climate Models developed by eight European Institutions (Bravo-Oviedo et al. 2010). Predictions indicated under SRES-A2 scenario showed a decreasing trend in forest productivity of P. pinaster Ait. but with some variability among regions and site quality classes, inasmuch as southern populations will be more affected.
This period is the consolidation of the research line in stand and dominant height growth modelling using climate variables (Bravo-Oviedo et al. 2011; Bravo et al. 2011; Mora et al. 2012; López-Senespleda et al. 2014) and the opening of a new search line about the impact of forest thinning in carbon sequestration (Ruiz-Peinado et al. 2013, 2014).